Quick take-down firearm

ABSTRACT

Quick take-down firearms and methods of using quick-take down firearms. The quick-take down includes an upper receiver coupling and a barrel coupling. The quick take-down can be unlocked by sliding a sliding lock collar in a translational motion to an unlocked position to release locking elements from a locked configuration. In the unlocked position, a barrel and handguard may be installed onto and removed from the upper receiver of the firearm. Releasing the sliding lock collar returns it to a locked position, securing the barrel and handguard to the upper receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent claims the benefit of U.S. non-provisional patent application Ser. No. 15/357,538, filed Nov. 21, 2016 for a “Quick Take-Down Firearm,” which claims the benefit of U.S. provisional patent application No. 62/314,758, filed Mar. 29, 2016 for a “Straight-in, rifle barrel attachment & detachment using a ball bearing positive lock,” the contents of both of which are incorporated in their entireties by this reference.

This patent also claims the benefit of U.S. provisional patent application No. 62/433,696, filed Dec. 13, 2016 for an “Upper receiver and barrel designed with integrated, straight-In, positive lock coupling,” the contents of which are incorporated in their entirety by this reference.

BACKGROUND

AR-15, AR Pistols, M4, M16 and similar prior art MILSPEC rifles cannot be quickly disassembled and reassembled where the rifle barrel connects to the upper receiver, a process which usually requires the use of specialized tools and a work-bench equipped with a vise. While there are some prior art systems that allow for in-field tool-less disassembly and reassembly of the barrel from the upper receiver, these systems are not effective or robust, are complicated to use, and do not allow for use of standard MILSPEC had guards and other accessories commonly used with these types of firearms.

SUMMARY

This patent is for quick-take down firearms and methods of using quick-take down firearms.

In one non-limiting example, the quick-take down includes an upper receiver coupling configured to be secured to an upper receiver threading of the firearm, the upper receiver coupling including several rotationally offset gas tube tunnels extending through the upper receiver coupling; further includes a rifle barrel coupling configured to be secured to a barrel of the firearm; and further includes a sliding lock collar configured to be slid in a translational motion between a locked position and an unlocked position, the sliding lock collar biased to the locked position; when the sliding lock collar is in the unlocked position the barrel of the firearm can be removed from and installed on the upper receiver; when the sliding lock collar is in the locked position and the barrel is installed on the upper receiver the upper receiver coupling is secured to the rifle barrel coupling thereby securing the barrel to the upper receiver.

In one non-limiting example, a method of assembly for a quick take-down firearm includes: sliding a sliding lock collar in a translational motion to an unlocked position to release a plurality of locking elements from a locked configuration, in which the sliding lock collar is biased away from the unlocked position towards a locked position; next, while the sliding lock collar is held at the unlocked position, inserting a barrel of the firearm into an upper receiver of the firearm, in which an upper receiver coupling is secured to threading of the upper receiver, the upper receiver coupling comprising a gas tube tunnel extending through a body of the upper receiver coupling and a barrel coupling is secured to the barrel; next inserting the barrel into the upper receiver further comprises inserting a barrel pin of the barrel into a notch of the upper receiver threading, and inserting a gas tube of the barrel through the gas tube tunnel of the upper receiver coupling; and next, after inserting the barrel into the upper receiver, releasing the sliding lock collar such that it slides in the translational motion to the locked position to secure the upper receiver coupling to the barrel coupling.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of a prior art firearm.

FIG. 2 shows the firearm of FIG. 1 with the barrel and handguard disassembled from the upper receiver.

FIG. 3 shows the upper receiver of the firearm of FIG. 1 in more detail.

FIGS. 4A-4B show and end of the barrel of the firearm of FIG. 1 in more detail.

FIG. 5A schematically shows an example of a quick take-down coupling installed on a firearm.

FIGS. 5B-5E show end and cross-sectional views of the quick take-down coupling of FIG. 5A.

FIG. 6 shows an example of an upper receiver coupling component in a disassembled condition.

FIGS. 7A-7D show an example of a body of an upper receiver coupling component.

FIGS. 8A-8C show an example of a sliding lock collar of an upper receiver coupling component.

FIGS. 8D-8E schematically show an example of an upper receiver coupling component in unlocked and locked configurations respectively.

FIGS. 9A-9C show an example of a face plate of an upper receiver coupling component.

FIGS. 10A-10C show an example of a barrel coupling component.

FIG. 11 schematically shows an example of a barrel coupling component mounted on a barrel.

FIG. 12 schematically shows an example of a protective cap for a gas tube and barrel end.

FIG. 13 shows an example of a quick take-down coupling that is integrated into the upper receiver and barrel of a firearm, shown with the barrel un-coupled from the upper receiver.

FIG. 14 shows the firearm of FIG. 13 with the barrel coupled to the upper receiver.

FIG. 15 shows the upper receiver of the firearm of FIG. 13.

FIG. 16 shows the components of the integrated upper receiver coupling of FIG. 13.

FIG. 17A-17B shows the integrated upper receiver coupling of FIG. 13 in more detail.

FIG. 18 shows the barrel of the firearm of FIG. 13.

FIG. 19 shows an end view of the barrel of FIG. 18.

FIG. 20 shows another example of a firearm with an integrated quick take-down coupling, shown with the barrel uncoupled from the upper receiver.

FIG. 21 shows the firearm of FIG. 20 with the barrel coupled to the upper receiver.

FIG. 22 shows another example of a barrel for a quick take-down firearm.

FIG. 23 shows a cross section of another example of a barrel for a quick take-down firearm.

DETAILED DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 show a prior art firearm, which, in this example, is an AR-15. The quick take-down couplings described in this patent are not limited to use with AR-15's, however, and may be used with a wide variety of firearms where it may be desirable to be able to quickly take down and assemble a firearm. As non-limiting examples, the quick take-down couplings of this patent may also be used with M4's, M16's, and similar MILSPEC rifles.

The firearm of FIGS. 1 and 2 includes an upper receiver 10, a barrel 12, and a handguard 14. FIG. 1 shows the firearm assembled with the barrel 12 and handguard 14 attached to the upper receiver 10. FIG. 2 shows the firearm disassembled with the barrel 12 and handguard 14 removed as a unit from the upper receiver 10.

FIG. 3 shows in more detail an example of a prior art upper receiver 10. The upper receiver 10 includes an opening 16 for receiving an end of the barrel 12, threads 18 surrounding the opening 16, a notch 20 in the threads 18, and reference surface 22 (e.g. the shoulder where threading 18 ends). FIG. 3 also shows another opening 24 in the upper receiver 10 for receiving a gas tube or piston that facilitates cycling of the firearm (FIG. 2 shows a gas tube 26).

FIGS. 4A and 4B show in more detail an example of a prior art barrel 12. The barrel 12 includes on its outer surface a reference surface 28 (e.g. a ridge extending around the barrel) and a pin 30.

In the prior art, the barrel 12 was attached to the upper receiver 10 by inserting the end of the barrel 12 into the upper receiver's opening 16 until the barrel reference surface 28 contacted the reference surface of the upper receiver 22 and the pin 30 was fully seated in the notch 20. Next, a barrel nut (not shown) would be threaded onto the threads 18 of the upper receiver 10 to secure the barrel 12 in the opening 16. A handguard (e.g. such as handguard 14 shown in FIGS. 1 and 2) could be secured by threading the handguard onto exterior threads of the barrel nut or in other manners.

Quick Take-Down Coupling Example

FIGS. 5A-5E show an example of a quick take-down coupling that can be used with the firearm of FIGS. 1-4 to provide quick and easy installation and removal of the barrel from the upper receiver. The quick take-down coupling of FIGS. 5A-5E includes an upper receiver coupling 32 and a barrel coupling 34. The upper receiver coupling 32 secures to the threads 18 of the upper receiver. The barrel coupling 34 secures to the barrel 12 proximate the reference surface 28 and pin 30. The quick take-down coupling has a locking mechanism, described in further detail below, for locking and unlocking the upper receiver coupling 32 from the barrel coupling 34, providing for quick and easy installation and removal of the barrel 12 from the upper receiver 10. FIGS. 5A-5E provide a general overview of the upper receiver coupling 32 and barrel coupling 34 components, and do not show all of the individual elements of those components.

FIGS. 6 through 9 show the upper receiver coupling 32 of FIG. 5 in further detail. Referring to FIG. 6, the upper receiver coupling 32 includes, from left to right, a body 36, locking elements 38, resilient element 40, sliding lock collar 42, and face plate 44. The resilient element 40 is shown in FIG. 6 as a coil spring, although other types of resilient elements may be used, such as a wave spring.

FIGS. 7A-7D show the body 36 of FIG. 6 in further detail. The body 36 includes an opening 46 extending through it from one end to the other. At least a portion of the opening 46 includes interior threading 48 (see FIG. 6) which is configured to engage the exterior threading 18 of the upper receiver 10. In other words, the pitch, thread angle, major diameter, minor diameter, etc. of the threading 48 of the body 36 is configured to correspond with the pitch, thread angle, major diameter, minor diameter, etc. of the threading 18 of the upper receiver 10. In some embodiments, the body threading 48 is MILSPEC or other standardized threading allowing it to be installed on a wide variety of commercially available firearms. The body 36 of FIGS. 7A-7D also includes through holes 50 around the perimeter of the body 36 for receiving set screws or similar items to further secure the upper receiver coupling 32 to the upper receiver threads 18. In some embodiments, the set screws used may be nylon or another relatively soft material to lessen the risk of damaging the upper receiver threads 18.

The body 36 of FIGS. 7A-7D further includes apertures 52 spaced around the body 36 configured to receive locking elements 38 (e.g. ball bearings) such that portions of the locking elements may protrude into the opening 46 of the body 36 when the upper receiver coupling 32 is in a locked configuration (discussed further below). As shown in FIG. 7D, the apertures taper so that, in cooperation with the shape of the locking elements 38, the amount of penetration of the locking elements 38 into the opening 46 is limited.

The body 36 of FIGS. 7A-7D further includes several tunnels 54 extending through the length of the body from one end to the other. The tunnels 54 are configured to allow passage of a gas tube or piston associated with the barrel 12 through the body 36 and into the opening 24 on the upper receiver. As shown in FIGS. 7A-7C, the tunnels 54 are rotationally offset from one another (in this example, there are four tunnels 54 spaced apart 90 degrees from adjacent tunnels 54) and also rotationally offset from the apertures 52 in the body 36. In this example, the tunnels 54 are rotationally offset to allow for proper alignment of one of the tunnels 54 with the opening 24 in the upper receiver 10 when the upper receiver coupling 32 is secured to the upper receiver threads 18 at a desired torque or within a desired torque range.

In other embodiments, tunnels are not necessary. For example, in some embodiments, the quick-take down system may be used with an AR Pistol or other firearm that uses direct blowback cycling, without the need for a gas tube or piston.

The body 36 of FIGS. 7A-7D further includes a flange or shoulder 56 and openings 58, the purposes of which will be described further blow.

FIGS. 8A-8C show the sliding lock collar 42 of FIG. 6 in further detail. The collar 42 has an opening extending through it with an innermost internal diameter of sufficient dimension to allow the collar 42 to fit over a portion of the body 36 in a sliding fashion. The collar 42 may be slid in a translational motion along the body 36 (e.g. straight along the body 36 without rotation of the collar 42 relative to the body 36).

The opening of collar 42 includes a recessed area terminating at shoulder 60 at one end of the collar 42. The recess is configured to contain the resilient element 40 shown in FIG. 6, with one end of the element 40 acting against shoulder 56 and the other end of the element 40 acting against shoulder 60 such that collar 42 is biased away from the shoulder 56 of body 36 towards the other end of the body 36.

The opening of collar 42 also includes a second recess at the other end of the collar 42. In this particular example, second recess is formed by ramped surface 62. When the collar 42 is biased away from the shoulder 56 of body 36, the ramped surface 62 acts on locking elements 38 to cause those elements to protrude into the opening 46 of body 36 (see FIG. 8D) in a locked position. When the collar 42 is pulled back against the bias of resilient element 40, the locking elements 38 are unlocked and can move out of the opening 46 (see FIG. 8E).

FIGS. 9A-9C show the face plate 44 of FIG. 6 in more detail. The face plate includes a central opening 64 and tunnel portions 66 corresponding to the opening 46 and tunnels 54 of body 36. The outer diameter of the face plate 44 is of sufficient size so that when it is secured to the end of body 36 (e.g. using fasteners passing through fastener openings 68 in face plate 44 and into openings 58 in body 36), the face plate 44 limits the sliding movement of collar 42 away from the shoulder 56 of body 36.

FIGS. 10A-10C show the barrel coupling 34 of FIG. 5 in more detail. The barrel coupling 34 includes an opening 70 extending through it for receiving the barrel 12 of a firearm. In the particular example shown, the opening 70 includes a recessed area 72 that partially or entirely receives a ridge on the barrel 12 such that the barrel coupling 34 can be slid over the barrel 12 and receive the barrel ridge in the recessed area 72 such that the reference surface 22 (e.g. a rear surface of the barrel ridge) is flush with or slightly proud of the end of barrel coupling 34 (see FIG. 11). Recessed area 72 can also be seen in FIGS. 5C-5E. Returning to FIGS. 10A-10C, the barrel coupling 34 includes fastener openings 74 for receiving fasteners to further secure the barrel coupling in position on the barrel 12.

The barrel coupling 34 further includes several locking element receivers 76 spaced apart from one another and configured and located to receive portions of locking elements 38 during use. In the particular example shown, the locking elements receivers 76 are depressions in the outer surface of the barrel coupling 34. In the particular example shown, the spaced apart locking elements 38 and locking element receivers 76 help to resist rotation of the movement or forces of the upper receiver coupling 32 relative to the barrel coupling 34 when the components are locked together.

The barrel coupling 34 further includes threads 78 on a portion of its outer surface. Threads 78 are not shown in FIG. 10 but are shown in FIG. 11. The pitch, thread angle, and other characteristics (e.g. major diameter, minor diameter) of the threads 78 of barrel coupling 34 are the same or substantially the same as the pitch, thread angle, and other characteristics of the threads 18 of upper receiver 10. Because these thread characteristics are the same or substantially the same, barrel and/or handguard nuts or other connectors useable with the upper receiver threads 18 are also useable with the barrel coupling threads 78, meaning that handguards and other components that were usable with the upper receiver 10 can still be used with the firearm after installation of the upper receiver coupling 32 and barrel coupling 34 without necessarily requiring modification of those components or additional adaptors.

FIG. 12 illustrates an example of a protective cap 82 for protecting the end of gas tube 26 (or a piston) when the firearm is disassembled.

Example Method of Installation

The following is one example of a method of installing the quick-take down coupling shown in FIGS. 5-12.

The upper receiver coupling 32 may be installed onto the upper receiver 10 by threading the upper receiver coupling 32 onto the upper receiver threads 18 to a desired torque and such that one of the tunnels 54 of the upper receiver coupling 32 is adequately aligned with the opening 24 in upper receiver 10. Set screws or other fasteners may be inserted into openings 50 in body 36 to further secure the upper receiver coupling 32 to the upper receiver threads 18.

The barrel coupling 34 may be installed onto the barrel 12 by sliding the coupling 34 onto the barrel until the barrel ridge is partially or entirely received in recessed area 72, with the reference surface 28 of the barrel ridge coplanar or just proud of the end of barrel coupling 34 and barrel pin 30 adjacent or proximate the barrel coupling 34. Set screws or other fasteners may be inserted into openings 74 in coupling 34 to further secure it to the barrel 12.

A handguard and/or barrel nut (e.g. 80 in FIG. 5A) may be threaded onto the barrel coupling 34 (in some instances, this may be done prior to securing the barrel coupling 34 to barrel 12). A gas tube (e.g. 26 in FIG. 5A) or piston may be installed on barrel 12, with an end of the gas tube or piston extending through an opening in the handguard/barrel nut 80, and a handguard (e.g. 14 in FIG. 5A) may be installed onto the handguard/barrel nut 80.

Example Method of Use

The following is one example of a method of using the quick-take down coupling shown in FIGS. 5-12 after installation onto a firearm.

Protective cap 82 may be removed from the end of gas tube 26 and barrel 12.

Sliding lock collar 42 may be slid using a translational motion (e.g. non-rotational) back towards the upper receiver 10 to an unlocked position that releases the locking elements 38 inside of the upper receiver coupling 32.

While the sliding lock collar 42 is held at the unlocked position, the barrel 12 may be inserted into the upper receiver 10. The barrel 12 is inserted until the barrel reference surface 28 contacts the upper receiver contact surface 22, with the barrel pin 30 seated in notch 20. During insertion of the barrel, gas tube 26 (or a piston) is also inserted through one of the tunnels 54 in the upper receiver coupling 32 and into opening 24 in the upper receiver 10. Once inserted, the locking element receivers 76 of the barrel coupling 34 are aligned with the locking elements 38 of the upper receiver coupling 32.

Once inserted, the sliding lock collar 42 is released such that resilient element 40 forces the sliding lock collar 42 back to a locked position, causing the locking elements 38 to engage the locking element receivers 76, securing the barrel 12 to the upper receiver 10.

The barrel 12 may be removed from the upper receiver 10 using the same procedure in reverse.

Integrated Quick Take-Down Coupling

FIGS. 13 through 21 show examples of firearms with quick-take down couplings that have been integrated into the firearm when it is manufactured. In FIGS. 13-21, the upper receiver coupling 132 and the barrel coupling 134 are integral components of the firearm that are incorporated into the upper receiver 122 and barrel 112 at the time of manufacture. In other examples, both components are not integral. For example, a quick take-down firearm could include an upper receiver with a non-integral coupling component (such as shown in FIGS. 5-6) and a barrel with an integral coupling component (such as shown in FIGS. 13-14). In other examples, the barrel coupling component could be non-integral and the upper receiver coupling component could be integral.

FIG. 16 shows the components of the upper receiver coupling 132. As with the upper receiver coupling 32 shown in FIG. 6, the upper receiver coupling 132 of FIG. 16—includes a body 136, locking elements 138, resilient element 140, sliding lock collar 142, and face plate 144. The body 136 may be an integral part of the upper receiver 122 (e.g. machined, molded, forged, etc. from the same material and at the same time as the rest of the upper receiver). Alternatively, the body 136 may be secured to the upper receiver 122 in other ways, such as how the body 36 is secured to the upper receiver 12 in earlier examples.

FIGS. 17A and 17B show additional features of the body 136. The body 136 includes a cavity with a stepped-down interior diameter having a larger interior diameter portion 202 that receives the coupling 134 of the barrel 112 and a smaller diameter portion 204 that receives an end of barrel 112. At the shoulder 206 where the cavity steps down in diameter there is an alignment protrusion receiver 208 (e.g. a notch) that receives an alignment protrusion (e.g. a pin) of the barrel 112, which is discussed further below. At the shoulder 206, there is also an opening 210 for receiving an anti-rotation feature, which is also discussed further below. As shown in FIGS. 17A and 17B, the body 136 also includes a tunnel 154 extending through the body, configured to allow passage of a gas tube or piston associated with the barrel 112 into the upper receiver 122.

FIGS. 18 and 19 show additional features of the barrel 112. The barrel 112 includes a portion 302 configured for insertion into the smaller diameter portion of the body 204 connected to the upper receiver 122. The barrel 112 also has a larger diameter coupling portion 304 including at least one depression (FIG. 18 shows multiple depressions) for engaging the locking elements 138 of the upper receiver coupling. At a shoulder where the barrel extension 302 meets the coupling portion 304 there is an alignment pin 306 and a counter-rotation feature 308 that fit into the notch 208 and opening 210 respectively in the body 136 of the upper receiver coupling, which properly align the barrel 112 to the upper receiver 122 (both rotationally and insertion depth) when assembled. The barrel also includes external threading 310 for securing a handguard to the barrel (e.g. as shown in FIGS. 20 and 21). In some embodiments, the external threading 310 is MILSPEC or other standardized threading allowing it to be used with standard barrel nuts or other threaded components for attaching a handguard to the barrel. As shown in FIG. 19, the barrel includes lugs 312 that interact with the lugs on the bolt when a round is chambered.

Barrel Extension with Quick Take-Down Coupling

FIGS. 22 and 23 show examples of barrels that have barrel extensions 402, in which the barrel extension 402 includes a quick take-down coupling 404.

In FIG. 22, the barrel extension 402 includes, from left to right, a cylindrical insertion surface 406 for insertion into the firearm's upper receiver, an alignment protrusion 408 (e.g. alignment pin) that fits into a notch of the upper receiver to rotationally align (and prevent rotation of) the barrel relative to the upper receiver, a reference surface 410 (e.g. a shoulder) limiting the insertion depth of the barrel into the upper receiver, the quick take-down coupling portion 404 of the barrel extension (including depressions 412) for engaging the locking elements of the quick take-down coupling of the upper receiver, and external threading 414 for securing a handguard. As also shown in FIG. 22, the barrel includes an elongated barrel portion 416 that secures to the barrel extension 402 by threading 418.

FIG. 23 show an example of a barrel extension 402 and part of an elongated barrel 416 in cross section. As shown in FIG. 23, internal features of the barrel extension 402 include lugs 420 for interacting with the lugs of a bolt when a round is chambered, and internal threading 422 for engaging the threading 418 on the elongated barrel. FIG. 23 also shows internal features of the elongated barrel 416 including the chamber 424 for receiving a round of ammunition and the bore 426 of the barrel.

The foregoing description is by way of example only, and does not limit in any way the scope of the present invention, which is set forth in the following claims. Additions, deletions, substitutions, and other modifications to the systems and methods described above may be made without departing from the scope or spirit of the present invention. 

1. A method of assembly for a quick take-down firearm, the method comprising: (a) sliding a lock in a translational motion from a locked position to an unlocked position to release a plurality of locking elements from a locked configuration, wherein a resilient member biases the lock away from the unlocked position towards the locked position; (b) inserting an end of a barrel of the firearm into an upper receiver of the firearm, seating an alignment protrusion into an alignment protrusion receiver, and connecting a gas tube of the barrel to the upper receiver; and (c) after inserting the end of the barrel into the upper receiver, allowing the resilient member to slide the lock to the locked position to return the plurality of locking elements to the locked configuration, securing the upper receiver to the barrel.
 2. The method of claim 1, wherein sliding the lock from the locked position to the unlocked position comprises sliding the lock without rotating the lock.
 3. The method of claim 2, wherein allowing the resilient member to slide the lock to the locked position comprises allowing the resilient member to slide the lock to the locked position such that the lock moves the locking elements inwardly towards the barrel.
 4. The method of claim 3, wherein allowing the resilient member to slide the lock to the locked position such that the lock moves the locking elements inwardly towards the barrel comprises allowing the resilient member to slide the lock to the locked position such that the lock moves the locking elements into at least one depression.
 6. The method of claim 5, wherein the at least one depression comprises a plurality of depressions around the barrel.
 7. The method of claim 5, wherein seating the alignment protrusion comprises seating an alignment pin of the barrel into a notch, the alignment pin and the notch limiting the rotation of the barrel relative to the upper receiver.
 8. The method of claim 7, wherein the at least one depression is located on a portion of the barrel having a larger diameter than a portion of the barrel where the alignment pin is located.
 9. The method of claim 2, wherein the lock comprises a sliding collar, wherein the sliding collar extends around the locking elements.
 10. The method of claim 9, wherein the sliding collar extends around the gas tube when the upper receiver is secured to the barrel.
 11. The method of claim 9, wherein when the upper receiver is secured to the barrel, the barrel extends into a first end and out of a second end of the sliding collar.
 12. A quick take-down firearm, comprising: (a) an upper receiver; (b) a barrel; (c) a handguard secured to the barrel; and (d) a lock collar configured to secure and release the barrel from the upper receiver, the lock collar translatable between a locked position in which the barrel and handguard are secured to the upper receiver and an unlocked position in which the barrel and handguard are removable from the upper receiver, the lock collar being biased towards the locked position by a resilient element, the lock collar located between the upper receiver and the handguard and extending around the barrel when the barrel and handguard are secured to the upper receiver.
 13. The quick-take down firearm of claim 12, further comprising a gas tube extending along the barrel, the lock collar extending around the barrel and the gas tube when the barrel and handguard are secured to the upper receiver.
 14. The quick take-down firearm of claim 12, further comprising a plurality of locking elements, the locking elements securing the barrel and upper receiver when the lock collar is in the locked position.
 15. The quick take-down firearm of claim 12, wherein the barrel comprises: (a) a portion for insertion into the upper receiver; (b) an alignment pin extending outwardly from a surface of the insertion portion; (c) external handguard threading; and (d) at least one depression for receiving the locking elements when the lock collar is located in the locked position.
 16. The quick-take down firearm of claim 15, wherein the at least one depression is located in a coupling portion between the insertion portion and the external handguard threading.
 17. The quick-take down firearm of claim 16, wherein the coupling portion has an exterior diameter greater than an exterior diameter of the insertion portion.
 18. The quick-take down firearm of claim 15, wherein the barrel further comprises an anti-rotation protrusion, wherein the upper receiver further comprises an opening configured to receive the anti-rotation protrusion when the barrel is secured to the upper receiver.
 19. A barrel extension for a quick take-down firearm, the barrel extension comprising: (a) on an exterior of the barrel extension, an insertion surface configured for insertion into an upper receiver of a quick take-down firearm, a reference surface configured to limit a depth of insertion of the insertion surface into the upper receiver, an alignment protrusion configured to rotationally align the barrel extension relative to the upper receiver, and at least one depression configured to receive one or more locking elements of a quick-take down coupling of the upper receiver; (b) in an interior of the barrel extension, a cavity extending through the barrel extension, and a plurality of bolt lugs extending into the cavity; and (c) the barrel extension configured for attachment to an elongated barrel.
 20. The barrel extension of claim 19, wherein the barrel extension is further configured to secure a handguard of the firearm.
 21. The barrel extension of claim 20, wherein threading on the exterior of the barrel extension is configured to secure the handguard to the barrel extension.
 22. The barrel extension of claim 19, wherein the alignment protrusion comprises an alignment pin extending from the insertion surface adjacent the reference surface.
 23. The barrel extension of claim 22, wherein the reference surface is located between the insertion surface and the at least one depression.
 24. The barrel extension of claim 23, wherein the at least one depression is located on a portion of the barrel extension having a larger exterior diameter than a portion of the barrel extension with the insertion surface.
 25. The barrel extension of claim 19, the interior of the barrel extension further comprising internal threading configured to secure the barrel extension to the elongated barrel.
 26. The barrel extension of claim 25, wherein the barrel extension is configured for attachment to an elongated barrel that comprises: a chamber configured to receive a round of ammunition, an elongated bore extending from the chamber, and exterior threading configured to secure the elongated barrel to the internal threading of the barrel extension.
 27. A barrel for a quick take-down firearm, the barrel comprising: (a) on an exterior of the barrel, an insertion surface configured for insertion into an upper receiver of a quick take-down firearm, a reference surface configured to limit a depth of insertion of the insertion surface into the upper receiver, an alignment protrusion configured to rotationally align the barrel relative to the upper receiver, and at least one depression configured to receive one or more locking elements of a quick-take down coupling of the upper receiver; (b) in an interior of the barrel, a cavity having a plurality of bolt lugs extending into the cavity, a chamber configured to receive a round of ammunition, and an elongated bore extending from the chamber; and (c) wherein the barrel is configured to secure a handguard of the firearm.
 28. The barrel extension of claim 27, wherein threading on the exterior of the barrel is configured to secure the handguard to the barrel.
 29. The barrel extension of claim 28, wherein the at least one depression is located between the reference surface and the threading on the exterior of the barrel. 